Transformer Loading Efficiency and Losses
The efficiency and losses of a transformer at a given load.
Example
You enter
- Transformer rating (kVA) 75
- No-load (core) loss (W) 200
- Full-load (copper) loss (W) 1200
- Load fraction (0-1) 0.75
- Power factor (0-1) 1
You get
- Efficiency 98.47%
- Peak-efficiency load 41
Checked against published worked examples from: University of Anbar (Alheety).
Details, formula, and sources
ScopeOutput kW = kVA x load x PF, total loss = the fixed no-load (core) loss plus the load^2 x full-load (copper) loss, efficiency = output / (output + loss). A 75 kVA unit with 200 W core and 1,200 W copper loss at 75% load runs 98.47% efficient, with peak efficiency near sqrt(200/1200) = 41% load; a lightly loaded oversized transformer suffers because the core loss becomes a bigger fraction of a small throughput. A design/screening aid; the manufacturer's test report governs.
Formula or tableoutput = kVA x load x pf; losses = (noload_w + load^2 x loadloss_w)/1000; efficiency = output/(output+losses); peak at load = sqrt(noload/loadloss).
Source and editionTransformer loading efficiency and losses, standard power-transformer practice (IEEE C57 loss definitions) by name; first-principles core-plus-copper loss model.
Free accessThe core-plus-copper loss model and the efficiency relation are first-principles; transformer test-report losses are manufacturer data.
What governsEstimate. AHJ and licensed professional govern.
API field nameskva_rating, noload_w, loadloss_w, load, pf, efficiency, max_eff_load
- Two-part loss fixed core loss + load^2 x full-load copper losstransformer loss model
- Efficiency output / (output + total loss), output = kVA x load x pffirst principles
- Peak load maximum efficiency at load = sqrt(no-load / full-load loss)loss-balance derivation